pi: handle lud-17 URI payment identifier

LNURL-W/P can also be encoded in lud-17 form instead of bech32.
https://github.com/lnurl/luds/blob/luds/17.md
e.g.
lnurlw://example.com/api/test123
lnurlp://example.com/api/test123

electrum/lnurl.py

@@ -21,6 +21,9 @@ from electrum.i18n import _
 _logger = get_logger(__name__)
 
 
+SUPPORTED_LNURL_SCHEMES = ('lnurlp', 'lnurlw')
+
+
 class LNURLError(Exception): pass
 
 class UntrustedLNURLError(LNURLError):